Extracted from Azócar (2013).
Rock glaciers in air photos and satellite images present particular visual features and distribution patterns that have been used by several authors to identify rock glaciers in mountain areas (Barsch, 1996; Roer & Nyenhuis, 2007):
- Generally, rock glaciers present a tongue or lobe shape, with ridges and furrows on their surface that are indicative of their present or past deformation; moreover, they exhibit a steep front slope near the angle of repose. The shape of a rock glacier is mainly controlled by its surrounding topography.
- Most rock glaciers are located underneath talus slopes and at the end of terminal moraines surrounded glacier cirques.
- Some rock glaciers can be located in a geomorphic continuum at the end of a glacier system, normally in the distal part of debris-covered glaciers.
- Frequently active, inactive and relict rock glaciers are situated in different altitudinal bands. Active and inactive rock glaciers are situated at higher altitudes than relict forms.
Even though rock glaciers can be easily detected visually, classification of their dynamic status (see section 2.7.2.3) as active, inactive and relict requires a more detailed analysis of several geomorphological and environmental characteristics. In general, the dynamic status of rock glaciers has been evaluated based on geomorphological criteria (i.e., surface relief, appearance of the rock glacier front), environmental attributes (i.e., the presence of vegetation) and direct measurements of velocity and thermal conditions (Janke et al., 2013). A steep front (>35°) with unstable rocks and without vegetation has usually been used as a characteristic indicative of an active rock glacier; in contrast, a smooth front slope with stable boulders indicates that a rock glacier is inactive (Burger et al., 1999). On the other hand, an irregular and collapsed surface due to thawing of the ice commonly indicates that a rock glacier is a relict form (Putnam & David, 2009).
In-situ measurements of surface velocity through GPS survey and photogrammetry permit the quantification of rock glacier creep. Based on this kinematic information, it is possible to distinguish an active glacier from an inactive or relict forms very easily; however, GPS measurements are not suitable for making a clear distinction between inactive and relict rock forms. BTS measurement and monitoring of GST are appropriate methods to distinguish between intact and relict forms but not between active and inactive forms (see section 2.9).
For this study, the relevance of different geomorphological, geomorphometric and environmental characteristics that indicate the dynamic status of rock glaciers is summarized in Table 2, based mainly on the studies of Roer & Nyenhuis (2007), Barsch (1996), Burger et al. (1999) and Janke et al. (2013). Each criterion presented in Table 2 can be used to evaluate a rock glacier’s dynamic status. The characteristics criteria were adapted for the specific environmental conditions of rock glaciers in the semi-arid Andes.
Table 1. Evaluation of geomorphological, geomorphometric and environmental characteristics for the determination of rock glacier activity in the semi-arid Chilean Andes (Slightly modified after Roer & Nyenhuis, 2007).
Slope angle of rock glacier front Slope angle: |
steep/flat |
Quantitative |
Not suitable |
Deficient |
Good |
Geomorphological appearance of rock glacier front |
Micro-scale geomorphic forms indicating movement |
Descriptive |
Very good |
Deficient |
Very good |
Tonal appearance of rock glacier front on air-photos or satellite images |
Presence of light tones on slope front |
Descriptive |
Very good |
Good |
Very good |
Vegetation or lichen abundance |
Spatial distribution |
Descriptive |
Not suitable |
Not suitable |
Not suitable |
Geomorphological appearances of the surface relief |
Presence of ridges and furrows |
Descriptive |
Deficient |
Deficient |
Good |
Appearance of rocks on rock the rock glacier surface |
Degree and position of rock weathering |
Descriptive |
Deficient |
Good |
Very good |
The stability of large rocks on the rock glacier surface |
Large rocks moveable by hand |
Descriptive |
Deficient |
Good |
Very good |
Ocurrence of ice outcrops |
Location of feature |
Descriptive |
Not suitable |
Very good |
Very good |
Occurrence of thermokarst |
Location of feature |
Descriptive |
Not suitable |
Very good |
Very good |
Basal Temperature of snow(BTS) |
Ground Surface Temperature (GST) |
Temperature measurements under a cover snow of at least 0.8 m |
Quantitative |
Not suitable |
Good |
Measurements of velocity |
GPS survey |
Quantitative |
Good |
Very good |
Very good |
Perennial snow patches |
Location of feature |
Descriptive |
Not suitable |
Not suitable / Good |
Not suitable |
Measurements of water temperature coming from the rock glacier |
Temperature measurements of spring water |
Descriptive |
Not suitable |
Good |
Good |
Main Citations
- Azócar, G. (2013). Modeling of permafrost distribution in the Semi-arid Chilean Andes, M.S. thesis, University of Waterloo, Canada, 160 pp.
- Barsch, D. (1996). Rockglaciers: Indicators for the present and former geoecology in high mountain environments. Berlin, Germany: Springer.
- Burger, K., Degenhardt, J., & Giardino, J. (1999). Engineering geomorphology of rock glaciers. Geomorphology, 31, 93-132.
- Janke, J., Regmi, N., Giardino, J., & Vitek, J. (2013). Rock Glaciers. In J. Schroder (Ed.), Treatise on Geomorphology (Vol. 8, pp. 238-273).
- Roer, I., & Nyenhuis, M. (2007). Rockglacier activity studies on a regional scale:comparison of geomorphological mapping and photogrammetric monitoring. Earth Surface Processes and Landforms, 32(12).
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